Zero dark sexy! Jessica Chastain recently told Us Weekly she'll be attending this Sunday's Academy Awards with her grandmother -- but that doesn't mean the actress, 35, doesn't have a special man in her life.

The redheaded Zero Dark Thirty star, 35, has been quietly seeing Gian Luca Passi, an Italian-born executive for French fashion brand Moncler. "They've been dating seriously for awhile now and Gian really likes her," a source tells Us. The twosome have made a pact to keep their relationship out of the spotlight. "He is a classy guy and completely agrees about respecting their relationship and not flaunting it," says the source of her man, recently seen taking in a performance of her Broadway show The Heiress.

Chastain spoke discreetly about her man during a recent appearance on Katie. When Katie Couricasked Chastain if she had a boyfriend, she demurred, "I do . . . I have a rule that I don't date actors so he's not in the business at all . . . He's in the fashion industry."

And on at last weekend's Writers' Guild Awards in L.A., Chastain -- up against Jennifer Lawrence, Emmanuelle Riva, Naomi Watts and Quvenzhane Wallis in the Best Actress category at this Sunday's Oscars -- couldn't help but gush a bit about her man at a backstage gifting suite.

Still, her hunk won't be by her side come Sunday. That'll be Chastain's grandmother. "Going with her, it's such a reminder to enjoy it," the Mama star told Us Weekly recently.

With that in mind, she stopped by the Kari Feinstein Style Lounge at the W Hollywood Hotel on Thursday. "She was so excited to grab electronic cigarettes from e-Puffer," an observer reveals of the second-time nominee who also swooped up dry shampoo from Dove and Nalukai Jewelry. "But she is trying to help her grandmother quit!"